Text Reference: Pages 206 – 215 in the Nelson Biology 12 textbook
SCIENTISTS WHO CONTRIBUTED IN DETERMINING THE STRUCTURE OF DNA (We should know the following about each scientist: Who? With what? What did it show?)
Friedrich Miescher (Late 1860s)
Lysed pus cells using a weak alkaline solution in order to isolate a unique chemical (non –protein) substance from the precipitated nuclei, which he called “nuclein”.
Determined that the “nuclein” was a storehouse for phosphorous
Phoebus Levene (Early 1900s)
His work was almost completely based on theoretical data.
Determined that nucleotides were linked by phosphodiester bonds (3’ and 5’)
Proposed that DNA was composed of tetranucleotides, a linked series of four nucleotides that were always the same.
Then, in 1938, he began to believe that DNA was a polymer with repeating units of tetranucleotides.
Frederick Griffith (1928)
Studied the S (smooth – disease causing) and the R (rough – harmless) strains of pneumococcus bacteria, which are both present in patients with pneumonia.
When he combined heat killed S-type with living R-type, it was able to infect a mouse and kill it. When injected alone, however, the heat killed S-type was unable to do any damage. This lead him to believe that some “principal” was transferred from S to R.
Joachim Hammerling (1930s)
Used Acetabularia mediterranea (who had circular caps) and Acetabularia crenulata (branched caps), which only had three parts, all of whom were visible to the naked eye.
Determined that the foot of an Acetabularia (where the nucleus resided) allowed it to regenerate its lost cap (a removed foot could not be regenerated) and that the foot of the Acetabularia determined the type of cap it would have, regardless of the type of stalk it had.
This led him to believe that the hereditary material was located in the nucleus.
Oswald Avery, along with Colin MacLeod and Maclyn McCarty (1944)
Used enzymes to remove the sugar coat, the proteins and then the RNA of a lysed and heat killed S-type strain of pneumococcus bacteria – one by one. They combined what was left with living R-type in a test tube, and waited to see if S-type would still be made. Even after removing all three, with only DNA left, S-type was still made. After removing the DNA, however, nothing happened.
This led them to conclude that DNA was the transforming principle.
Erwin Chargaff (1949)
By taking samples of DNA from different cells, he discovered that the amount of adenine = thymine and that the amount of guanine = cytosine. ( Purines (A,G) = Pyrimidines (C,G)). This later becomes “Chargaff’s Rule”.
Alfred Hershey and Martha Chase (1952) § Worked with bacteriophages, which are composed of DNA and a protein coat. § Produced phages with radioactive S-35 labeled protein coats (there is no S in DNA), which, when allowed to reproduce, produced phages with noradioactive coats. Then, they used radioactive P -32 to label the DNA (there is P in DNA, but not protein), which when injected in to a cell for reproduction, also produces viruses with radioactive DNA. .
Rosalind Franklin (1953) § Using x-ray crystallography, she produced an x-ray diffraction pattern of DNA, which suggested that DNA took on the shape of a double helix.
James Watson and Francis Crick (1953) § Using Rosalind Franklin’s and Chargaff’s work, they deduced the structure of DNA and built their famous model of the double helix structure. § They (along with Maurice Wilkins) were awarded a Nobel Prize for their efforts in 1962.
DNA STRUCTURE:
external image dna_double_helix_structure.jpg
Image taken from Pearson Education. We did a similar activity in class where we made a model similar to the one in the middle.
A double helix (2nm in diameter).
Turns clockwise.
Makes one complete turn every 10 nucleotides (3.4nm)
One strand goes from 5’ (phosphate) to the 3’ carbon (sugar) and the complimentary strand goes from the 3’ to the 5’. The strands run antiparellel to each other.
Nucleotides are composed of a phosphate group, a deoxyribose sugar and a nitrogenous base.
There are four nitrogenous bases, adenine (A) and guanine (G) which are purines (double ringed bases), and cytosine (C) and thymine (T), which are pyrmidines (single ringed bases).
A pairs with T and C pairs with G. This is called complementary base pairing.
Homework: Complete the review package and study for the quest on DNA structure this Wednesday, March 30.
Additional Links:
http://www.dnai.org/index.htm(This is the website I presented in class – it’s a great website with lots of animations, videos and games to help you understand not only the structure of DNA, but also DNA replication!
4.3 DNA REPLICATION NICOLE SAUNDERS MARCH 24 AND 28
The DNA replication song
DNA Replicates Semiconservatively
What does this mean?
- semiconservative is the process of replication in which each DNA molecule is composed of one parent strand and one new
synthesized strand
dna.jpg
The Process of DNA Replication
- this begins when proteins bind at a specific site of the DNA known as the replication orgin
- the DNA of prokaryotes usually only has one replication orgin
- the DNA of eukaryotes has multiple origins of replication
- the two strands of DNA cannot be simply pulled apart because they are held together by hydrogen bonds and they form a double
helix
-an enzyme called DNA helicase unwinds the double helix by breaking the hydrogen bonds between the base pairs
- single-standed binding proteins then bind to the exposed DNA single strands and block the hydrogen bonds from coming back
together
-once the stands unwind it adds tension to the coiled end, and enzyme known as DNA gyrase relives any tension that is brought on; it cuts both strands of DNA, allowing them to swivel around each other, and then it reseals the cut strands
- the replication fork is where the enzymes replicating a DNA molecule are bound to an untwisted, single stranded DNA
-the leading stand always builds towards the fork
-the lagging stands always builds away from the fork
-BUILDS FROM 5'-3'
DNA Replication Process
Building Complementary Stands
-in prokaryotes, DNA polymerase I,II,III are the three enzymes that aid in replication and repair
-in eukaryotes, there are five enzymes used Important Terms: Primase: The enzyme that builds RNA primers Leading Strand: the new strand of DNA that is synthesized continuously throughout the replication Lagging Strand: the new strand of DNA that is synthesized in small fragments, which are later joined together Okazaki Fragments: short fragments of DNA that are a result of the synthesis of the lagging strand DNA Ligase: the enzyme that joins the DNA fragments together
SUMMARY:
Steps of DNA Replication
The next we have to do is to shed light into the mystery of the steps of DNA Replicationof the Eykaryotes.
1)The first major step for the DNA Replication to take place is the breaking of hydrogen bonds between bases of the two antiparallel strands. The unwounding of the two strands is the starting point. The splitting happens in places of the chains which are rich in A-T. That is because there are only two bonds between Adenine and Thymine (there are three hydrogen bonds between Cytosine and Guanine). Helicase is the enzyme that splits the two strands. The initiation point where the splitting starts is called "origin of replication".The structure that is created is known as "Replication Fork".
step1.jpg
2) One of the most important steps of DNA Replication is the binding of RNA Primase in the the initiation point of the 3'-5' parent chain. RNA Primase can attract RNA nucleotides which bind to the DNA nucleotides of the 3'-5' strand due to the hydrogen bonds between the bases. RNA nucleotides are the primers (starters) for the binding of DNA nucleotides.
3) The elongation process is differe
step2.jpg
nt for the 5'-3' and 3'-5' template. a)5'-3' Template: The 3'-5' proceeding daughter strand -that uses a 5'-3' template- is called leading strand because DNA Polymerase ä can "read" the template and continuously adds nucleotides (complementary to the nucleotides of the template, for example Adenine opposite to Thymine etc).
step3.jpg
b)3'-5'Template: The 3'-5' template cannot be "read" by DNA Polymerase ä. The replication of this template is complicated and the new strand is called lagging strand. In the lagging strand the RNA Primase adds more RNA Primers. DNA polymerase å reads the template and lengthens the bursts. The gap between two RNA primers is called "Okazaki Fragments".
The RNA Primers are necessary for DNA Polymerase å to bind Nucleotides to the 3' end of them. The daughter strand is elongated with the binding of more DNA nucleotides.
step4.jpg
4) In the lagging strand the DNA Pol I -exonuclease- reads the fragments and removes the RNA Primers. The gaps are closed with the action of DNA Polymerase (adds complementary nucleotides to the gaps) and DNA Ligase (adds phosphate in the remaining gaps of the phosphate - sugar backbone).
step5.jpg
5) The last step of DNA Replication is the Termination. This process happens when the DNA Polymerase reaches to an end of the strands. We can easily understand that in the last section of the lagging strand, when the RNA primer is removed, it is not possible for the DNA Polymerase to seal the gap (because there is no primer). So, the end of the parental strand where the last primer binds isn't replicated. These ends of linear (chromosomal) DNA consists of noncoding DNA that contains repeat sequences and are called telomeres. As a result, a part of the telomere is removed in every cycle of DNA Replication.
6) The DNA Replication is not completed before a mechanism of repair fixes possible errors caused during the replication. Enzymes like nucleases remove the wrong nucleotides and the DNA Polymerase fills the gaps.
HOMEWORK: -complete the crossword review package to take up tomorrow -test on Thursday for sections 4.1,4.2,4.3
March 30, 2011
Megan Matkowski
Topic: Test Review
Remember test this Thursday, March 31st 2011
Things to know!
• History → DNA vs. Protein debate → SCIENTISITS: Friedrich Misher, Phoebus Levene, Joachim Hammerling, Oswald Avery, Fred Griffith, Colin MacLead, Maclyn McCarty, Alfred D. Hershey, Martha Chase, Erwin Chargaff, Rosalind Franklin, James Watson and Francis Crick.
→ Refer to your notes, textbook (Note that, our textbooks don't really go into great detail or mention some of the people), or look above to DNA structure notes posted by Virginia.
→ Key ideas!! Who? What? did they use? What did they show? What did they do?
(below is a template that might help organize these key ideas)
We all know that, DNA genes codes for proteins. Well how do we get there? We get there by......
PROTEIN SYNTHESIS !! In other words, the process of translation and transcription.
Basics of Protein Synthesis:
1) DNA transcribes to mRNA (messenger RNA)
Sidenote, couple things we need to know about transcription process :
-Messenger complimentality plays a role in RNA.
-Recall, that in RNA we find urical not tymine. Therefore, complement of Adiene is Urical .
2) mRNA is made in the nucleus which can travel to ribosomes where it will be translated to polypeptide or protein.
3) Information carried from the mRNA will translate to the "language of amino acids"
Sidenote: amino acids use 3 letter codes.
Summary: DNA -> language of mRNA (transcription process)
Where; the mRNA travels from the nucleus to the ribosomes where the information will be translated into the information essential for a polypeptide.
April 4-6, 2011 Arlanna Pugh and Connor Dorval 5.2-5.4 Protein Synthesis: Text Reference: Pages 237 - 254 in the Nelson Biology 12 Textbook DNA --------> RNA --------> Protein (Polypeptide)
Transcription:copying of DNA info into messenger RNA
· Where: Nucleus
· What: DNA to mRNA
Initiation:
-RNA polymerase binds to a site on DNA just before the start of the
gene, known as the promoter region.
-Promoter region is high in adenine and thymine, which contain
only two Hydrogen bonds, compared to the three shared by guanine
and cytosine. This reduces the amount of energy required to separate
the double helix.
Elongation:
-RNA polymerase builds single stranded mRNA in the 5' to 3' direction.
-No primer required.
-Promoter region is not transcribed.
-The strand of DNA being built upon by RNA Polymerase is called the
template strand, the other DNA strand is called the coding strand,
since the mRNA transcript will be identical in sequence to it (with
uracil replacing thymine).
Termination:
-A stop/terminator sequence is reached; mRNA disassociates.
-RNA polymerase, being an enzyme, can then be reused on another
Translation:ribosomes use mRNA as a blueprint to synthesize a protein composed of amino acids · Where: Cytoplasm (Ribosomes) · What: mRNA to Polypeptide (protein)
Initiation: -Ribosome recognizes a site on the mRNA (start codon, which almost always codes for methionine) Elongation: -tRNA delivers amino acids for every 3 bases (codon). -Starts by delivering methionine to peptide (P) site. -Each succesive amino acid is delivered to the acceptor (A) site. -A peptide bond is formed between the amino acids in the A and P sites. -The amino acid in the P site is then released from the ribosome, although is still attached to the succeeding amino acid. -The amino acid in the A site then moves to the P site, allowing another amino acid to be delivered to the A site. In this way, a chain of amino acids joined by peptide bonds (Polypeptide) is formed. -Note: It is the aminoacyl-tRNA (aminoacyl: amino acid carrying) that bonds to the A and P sites, with the amino acid itself attached to the other end, away from the actual mRNA. Once the amino acid joins the polypeptide chain, the tRNA is released and is able to recover another amino acid. Termination: -A stop codon is reached. The stop codon is a codon that does not code for any amino acid, and therefore does not attract an aminoacyl-tRNA. This causes a delay in translation. -This delay signals a protein known as a release factor to detach the polypeptide chain from the ribosome, terminating translation.
Ribonucleic Acid: Important Points: · Single stranded · Bases: adenine, uracil, cytosine, guanine · Contains ribose sugar · Found in nucleus AND cytoplasm (mRNA)
Messenger RNA (mRNA): · Length: Varies · Job: o Intermediary between DNA and the ribosomes o Translated into protein by ribosomes · Created: RNA gene version encoded by single strand DNA
Transfer RNA (tRNA): · Length: Very short (70 - 90 base pairs long) · Job: Delivery system of amino acids to ribosomes as they synthesize proteins
Ribosomal RNA (rRNA): · Length: Varies · Job: Binds with proteins to form the ribosomes
Genetic Code Important Points: · 20 amino acids in proteins; 4 bases in mRNA · 3 nucleotides = 1 codon = 1 amino acid (4^3 = 64 possibilities) · More than 1 codon for a single amino acid o Redundancy minimizes errors (chances for mutations) · Start codon: AUG (methionine) · Stop codons: UAA, UAG, UGA
Housekeeping Genes – Genes needed in a cell and are constantly being transcribed and translated.
Operon – Cluster of genes under the control of one promoter and one operator.
Operator – Regulatory sequences of DNA to which a protein repressor binds.
Lac Operon – Operon where the genes collectively code for the enzymes and proteins required for a bacterial cell to use lactose as a nutrient.
Lac I Protein – A repressor protein that binds to the Lac Operon operator preventing RNA polymerase from transcribing the Lac Operon genes.
Repressor Protein – Regulatory molecules that bind to an operator site and prevent transcription of an Operon.
Inducers – A molecule that binds to a repressor protein and causes a change in shape, resulting in the repressor protein falling off the operator.
trp Operon – A cluster of genes that govern the synthesis of the necessary enzymes required to synthesize the amino acid tryptophan.
Compressor – A molecule (usually the product of an Operon) that binds to a repressor to activate it.
The Lac Operon: The Lac Operon is a cluster of genes that codes for proteins involved in the metabolism of lactose. When lactose is not present in the cell environment, the Lac I Protein binds to the Lac Operator, covering part of the promoter end, stopping transcription. If lactose is introduced into the cell environment, the lactose binds to the Lac I Protein, changing its shape so that it falls off the operator and transcription can continue.
The trp Operon: The trp Operon is opposite to the Lac Operon, with regards to regulation of production. When the levels of Lactose are low, the repressor protein binds to the operator, halting transcription. With the trp Operon, when the levels of tryptophan are low, transcription occurs at a high rate. The trp Operon consists of five genes, which code for five polypeptides that produce three enzymes needed to synthesize tryptophan. When levels of tryptophan are high, the amino acids bind to the trp protein, altering its shape so transcription can continue. The tryptophan acts as a compressor and binds to the tryptophan repressor.
Sample DNA Quiz
DNA Structure
http://learn.genetics.utah.edu/
Article about Crick's Letters
http://www.nytimes.com/2010/09/30/science/30crick.html?_r=3&hp
Ted Talk: James Watson
http://www.ted.com/talks/lang/eng/james_watson_on_how_he_discovered_dna.html
DNA Replication Videos
http://www.youtube.com/watch?v=aSILNKbhNLg&feature=related
http://www.youtube.com/watch?v=CRTXxXHBM3U&feature=channel
Biotechnology Tools and Techniques Lesson Sign-Up
Lactose and Tryptophan Operons
http://www.sumanasinc.com/webcontent/animations/content/lacoperon.html
http://bcs.whfreeman.com/thelifewire/content/chp13/1302002.html
Arlanna Pugh and Rabeea Fatima: Gel Electrophoresis Powerpoint Presentation
Way to Glow Results
March 23, 2011
DNA Fingerprinting Lab Results
Virginia Lee
Topic: DNA Structure
Text Reference: Pages 206 – 215 in the Nelson Biology 12 textbook
SCIENTISTS WHO CONTRIBUTED IN DETERMINING THE STRUCTURE OF DNA
(We should know the following about each scientist: Who? With what? What did it show?)
Friedrich Miescher (Late 1860s)
Phoebus Levene (Early 1900s)
Frederick Griffith (1928)
Joachim Hammerling (1930s)
Oswald Avery, along with Colin MacLeod and Maclyn McCarty (1944)
Erwin Chargaff (1949)
Alfred Hershey and Martha Chase (1952)
§ Worked with bacteriophages, which are composed of DNA and a protein coat.
§ Produced phages with radioactive S-35 labeled protein coats (there is no S in DNA), which, when allowed to reproduce, produced
phages with noradioactive coats. Then, they used radioactive P -32 to label the DNA (there is P in DNA, but not protein),
which when injected in to a cell for reproduction, also produces viruses with radioactive DNA.
.
Image taken from: http://knight.noble-hs.sad60.k12.me.us/content/exploringLife/text/chapter11/concept11.1.html
§ With this experiment, it was determined that DNA was the hereditary material - not proteins.
Rosalind Franklin (1953)
§ Using x-ray crystallography, she produced an x-ray diffraction pattern of DNA, which suggested that DNA took on the shape of a
double helix.
James Watson and Francis Crick (1953)
§ Using Rosalind Franklin’s and Chargaff’s work, they deduced the structure of DNA and built their famous model of the double helix
structure.
§ They (along with Maurice Wilkins) were awarded a Nobel Prize for their efforts in 1962.
DNA STRUCTURE:
Homework: Complete the review package and study for the quest on DNA structure this Wednesday, March 30.
Additional Links:
4.3 DNA REPLICATION
NICOLE SAUNDERS
MARCH 24 AND 28
The DNA replication song
DNA Replicates Semiconservatively
What does this mean?
- semiconservative is the process of replication in which each DNA molecule is composed of one parent strand and one new
synthesized strand
The Process of DNA Replication
- this begins when proteins bind at a specific site of the DNA known as the replication orgin
- the DNA of prokaryotes usually only has one replication orgin
- the DNA of eukaryotes has multiple origins of replication
- the two strands of DNA cannot be simply pulled apart because they are held together by hydrogen bonds and they form a double
helix
-an enzyme called DNA helicase unwinds the double helix by breaking the hydrogen bonds between the base pairs
- single-standed binding proteins then bind to the exposed DNA single strands and block the hydrogen bonds from coming back
together
-once the stands unwind it adds tension to the coiled end, and enzyme known as DNA gyrase relives any tension that is brought on; it cuts both strands of DNA, allowing them to swivel around each other, and then it reseals the cut strands
- the replication fork is where the enzymes replicating a DNA molecule are bound to an untwisted, single stranded DNA
-the leading stand always builds towards the fork
-the lagging stands always builds away from the fork
-BUILDS FROM 5'-3'
DNA Replication Process
Building Complementary Stands
-in prokaryotes, DNA polymerase I,II,III are the three enzymes that aid in replication and repair
-in eukaryotes, there are five enzymes used
Important Terms:
Primase: The enzyme that builds RNA primers
Leading Strand: the new strand of DNA that is synthesized continuously throughout the replication
Lagging Strand: the new strand of DNA that is synthesized in small fragments, which are later joined together
Okazaki Fragments: short fragments of DNA that are a result of the synthesis of the lagging strand
DNA Ligase: the enzyme that joins the DNA fragments together
SUMMARY:
Steps of DNA Replication
The next we have to do is to shed light into the mystery of the steps of DNA Replicationof the Eykaryotes.
1)The first major step for the DNA Replication to take place is the breaking of hydrogen bonds between bases of the two antiparallel strands. The unwounding of the two strands is the starting point. The splitting happens in places of the chains which are rich in A-T. That is because there are only two bonds between Adenine and Thymine (there are three hydrogen bonds between Cytosine and Guanine). Helicase is the enzyme that splits the two strands. The initiation point where the splitting starts is called "origin of replication".The structure that is created is known as "Replication Fork".
2) One of the most important steps of DNA Replication is the binding of RNA Primase in the the initiation point of the 3'-5' parent chain. RNA Primase can attract RNA nucleotides which bind to the DNA nucleotides of the 3'-5' strand due to the hydrogen bonds between the bases. RNA nucleotides are the primers (starters) for the binding of DNA nucleotides.
3) The elongation process is differe
b)3'-5'Template: The 3'-5' template cannot be "read" by DNA Polymerase ä. The replication of this template is complicated and the new strand is called lagging strand. In the lagging strand the RNA Primase adds more RNA Primers. DNA polymerase å reads the template and lengthens the bursts. The gap between two RNA primers is called "Okazaki Fragments".
The RNA Primers are necessary for DNA Polymerase å to bind Nucleotides to the 3' end of them. The daughter strand is elongated with the binding of more DNA nucleotides.
4) In the lagging strand the DNA Pol I -exonuclease- reads the fragments and removes the RNA Primers. The gaps are closed with the action of DNA Polymerase (adds complementary nucleotides to the gaps) and DNA Ligase (adds phosphate in the remaining gaps of the phosphate - sugar backbone).
5) The last step of DNA Replication is the Termination. This process happens when the DNA Polymerase reaches to an end of the strands. We can easily understand that in the last section of the lagging strand, when the RNA primer is removed, it is not possible for the DNA Polymerase to seal the gap (because there is no primer). So, the end of the parental strand where the last primer binds isn't replicated. These ends of linear (chromosomal) DNA consists of noncoding DNA that contains repeat sequences and are called telomeres. As a result, a part of the telomere is removed in every cycle of DNA Replication.
6) The DNA Replication is not completed before a mechanism of repair fixes possible errors caused during the replication. Enzymes like nucleases remove the wrong nucleotides and the DNA Polymerase fills the gaps.
Steps 1-6 found at: http://www.dnareplication.info/stepsofdnareplication.php
HOMEWORK:
-complete the crossword review package to take up tomorrow
-test on Thursday for sections 4.1,4.2,4.3
March 30, 2011
Megan Matkowski
Topic: Test Review
Remember test this Thursday, March 31st 2011
Things to know!
• History
→ DNA vs. Protein debate
→ SCIENTISITS: Friedrich Misher, Phoebus Levene, Joachim Hammerling, Oswald Avery, Fred Griffith, Colin MacLead, Maclyn McCarty, Alfred D. Hershey, Martha Chase, Erwin Chargaff, Rosalind Franklin, James Watson and Francis Crick.
→ Refer to your notes, textbook (Note that, our textbooks don't really go into great detail or mention some of the people), or look above to DNA structure notes posted by Virginia.
→ Key ideas!! Who? What? did they use? What did they show? What did they do?
(below is a template that might help organize these key ideas)
• Structure of DNA
• DNA Replication
Introduction to Protein Synthesis and Section 5.1: One Gene- One Polypeptide(NOT FINISHED YET)
Text Reference: Pages 232-236 in the Nelson Biology Textbook
So far we've been learning about DNA and it's structure, now we will be moving on to PROTEIN SYNTHESIS, woo!(take a look at this diagram)
We all know that, DNA genes codes for proteins. Well how do we get there? We get there by......
PROTEIN SYNTHESIS !! In other words, the process of translation and transcription.
Basics of Protein Synthesis:
1) DNA transcribes to mRNA (messenger RNA)
Sidenote, couple things we need to know about transcription process :
-Messenger complimentality plays a role in RNA.
-Recall, that in RNA we find urical not tymine. Therefore, complement of Adiene is Urical .
2) mRNA is made in the nucleus which can travel to ribosomes where it will be translated to polypeptide or protein.
3) Information carried from the mRNA will translate to the "language of amino acids"
Sidenote: amino acids use 3 letter codes.
Summary: DNA -> language of mRNA (transcription process)
Where; the mRNA travels from the nucleus to the ribosomes where the information will be translated into the information essential for a polypeptide.
April 4-6, 2011
Arlanna Pugh and Connor Dorval
5.2-5.4 Protein Synthesis:
Text Reference: Pages 237 - 254 in the Nelson Biology 12 Textbook
DNA --------> RNA --------> Protein (Polypeptide)
Transcription: copying of DNA info into messenger RNA
· Where: Nucleus
· What: DNA to mRNA
Initiation:
-RNA polymerase binds to a site on DNA just before the start of the
gene, known as the promoter region.
-Promoter region is high in adenine and thymine, which contain
only two Hydrogen bonds, compared to the three shared by guanine
and cytosine. This reduces the amount of energy required to separate
the double helix.
Elongation:
-RNA polymerase builds single stranded mRNA in the 5' to 3' direction.
-No primer required.
-Promoter region is not transcribed.
-The strand of DNA being built upon by RNA Polymerase is called the
template strand, the other DNA strand is called the coding strand,
since the mRNA transcript will be identical in sequence to it (with
uracil replacing thymine).
Termination:
-A stop/terminator sequence is reached; mRNA disassociates.
-RNA polymerase, being an enzyme, can then be reused on another
gene.
Animation: http://www.dnalc.org/resources/3d/12-transcription-basic.html
Translation: ribosomes use mRNA as a blueprint to synthesize a protein composed of amino acids· Where: Cytoplasm (Ribosomes)
· What: mRNA to Polypeptide (protein)
Initiation:
-Ribosome recognizes a site on the mRNA (start codon, which almost
always codes for methionine)
Elongation:
-tRNA delivers amino acids for every 3 bases (codon).
-Starts by delivering methionine to peptide (P) site.
-Each succesive amino acid is delivered to the acceptor (A) site.
-A peptide bond is formed between the amino acids in the A and P
sites.
-The amino acid in the P site is then released from the ribosome,
although is still attached to the succeeding amino acid.
-The amino acid in the A site then moves to the P site, allowing
another amino acid to be delivered to the A site. In this way, a
chain of amino acids joined by peptide bonds (Polypeptide) is formed.
-Note: It is the aminoacyl-tRNA (aminoacyl: amino acid carrying) that
bonds to the A and P sites, with the amino acid itself attached to the
other end, away from the actual mRNA. Once the amino acid joins the
polypeptide chain, the tRNA is released and is able to recover another
amino acid.
Termination:
-A stop codon is reached. The stop codon is a codon that does not code
for any amino acid, and therefore does not attract an aminoacyl-tRNA.
This causes a delay in translation.
-This delay signals a protein known as a release factor to detach the
polypeptide chain from the ribosome, terminating translation.
Animation: http://www.biostudio.com/demo_freeman_protein_synthesis.htm
Ribonucleic Acid:Important Points:
· Single stranded
· Bases: adenine, uracil, cytosine, guanine
· Contains ribose sugar
· Found in nucleus AND cytoplasm (mRNA)
Messenger RNA (mRNA):
· Length: Varies
· Job:
o Intermediary between DNA and the ribosomes
o Translated into protein by ribosomes
· Created: RNA gene version encoded by single strand DNA
Transfer RNA (tRNA):
· Length: Very short (70 - 90 base pairs long)
· Job: Delivery system of amino acids to ribosomes as they synthesize proteins
Ribosomal RNA (rRNA):
· Length: Varies
· Job: Binds with proteins to form the ribosomes
Genetic Code
Important Points:
· 20 amino acids in proteins; 4 bases in mRNA
· 3 nucleotides = 1 codon = 1 amino acid (4^3 = 64 possibilities)
· More than 1 codon for a single amino acid
o Redundancy minimizes errors (chances for mutations)
· Start codon: AUG (methionine)
· Stop codons: UAA, UAG, UGA
Overview of Both Transcription and Translation (*Very Helpful Website):
http://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio%20101/bio%20101%20lectures/protein%20synthesis/protein.htm
Operons
Ryan Smith
April 27, 2011
Definitions:
Housekeeping Genes – Genes needed in a cell and are constantly being transcribed and translated.
Operon – Cluster of genes under the control of one promoter and one operator.
Operator – Regulatory sequences of DNA to which a protein repressor binds.
Lac Operon – Operon where the genes collectively code for the enzymes and proteins required for a bacterial cell to use lactose as a nutrient.
Lac I Protein – A repressor protein that binds to the Lac Operon operator preventing RNA polymerase from transcribing the Lac Operon genes.
Repressor Protein – Regulatory molecules that bind to an operator site and prevent transcription of an Operon.
Inducers – A molecule that binds to a repressor protein and causes a change in shape, resulting in the repressor protein falling off the operator.
trp Operon – A cluster of genes that govern the synthesis of the necessary enzymes required to synthesize the amino acid tryptophan.
Compressor – A molecule (usually the product of an Operon) that binds to a repressor to activate it.
The Lac Operon:
The Lac Operon is a cluster of genes that codes for proteins involved in the metabolism of lactose. When lactose is not present in the cell environment, the Lac I Protein binds to the Lac Operator, covering part of the promoter end, stopping transcription. If lactose is introduced into the cell environment, the lactose binds to the Lac I Protein, changing its shape so that it falls off the operator and transcription can continue.
http://www.youtube.com/watch?v=iPQZXMKZEfw
The trp Operon:
The trp Operon is opposite to the Lac Operon, with regards to regulation of production. When the levels of Lactose are low, the repressor protein binds to the operator, halting transcription. With the trp Operon, when the levels of tryptophan are low, transcription occurs at a high rate. The trp Operon consists of five genes, which code for five polypeptides that produce three enzymes needed to synthesize tryptophan. When levels of tryptophan are high, the amino acids bind to the trp protein, altering its shape so transcription can continue. The tryptophan acts as a compressor and binds to the tryptophan repressor.
http://www.youtube.com/watch?v=VNok-vF03aI&feature=related
· Operons DO NOT code for proteins
· Operons are only found in PROKARYOTES
· Operons are used because they let the cell use LESS energy